**Core Concept**
Argon laser is a type of laser used in ophthalmology for treating various conditions, including diabetic retinopathy, retinal tears, and retinal detachment. The laser emits a beam of light that is selectively absorbed by the retinal pigment epithelium, causing thermal damage to the underlying tissue.

**Why the Correct Answer is Right**
The side effects of argon laser treatment are due to the thermal damage caused by the laser to the surrounding tissue. **Hypopigmentation** is a common side effect, as the laser can damage the melanocytes, leading to a decrease in pigmentation. **Crusting** occurs as a result of the thermal damage to the epithelial layer, causing the formation of a crust or scab on the surface of the eye. **Keloid formation** is a rare but possible side effect, where the laser causes excessive collagen deposition, leading to the formation of a keloid scar.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypopigmentation is a recognized side effect of argon laser treatment, so this option is correct but not one of the distractors.
**Option B:** While crusting is a side effect of argon laser treatment, it is not as severe or common as hypopigmentation.
**Option C:** Keloid formation is a rare side effect of argon laser treatment, and it is not as well-documented as hypopigmentation.

**Clinical Pearl / High-Yield Fact**
When using argon laser for ophthalmic conditions, it is essential to carefully control the laser settings and duration to minimize the risk of side effects. A thorough pre-treatment evaluation and post-treatment follow-up are crucial to detect any potential complications early on.

**✓ Correct Answer: D. All the above**